. Compendium of meteorology. Meteorology. (b) Fig. 12.— (a) Harmonic dial (with probable-error circles) for the annual mean lunar semidiurnal variations in the north- ward and eastward components of wind velocity at Mauritius, from about 16 years' bihourly data. (&) Harmonic dial for the corresponding annual mean solar semidiurnal variations. Note the tenfold scale difference between the two diagrams. ent. The speed scale in Fig. 13a (lunar) is ten times more open than that for Fig. 136 (solar). The diagram Fig. 13a is, of course, not well determined. The corresponding semidiurnal paths of
. Compendium of meteorology. Meteorology. (b) Fig. 12.— (a) Harmonic dial (with probable-error circles) for the annual mean lunar semidiurnal variations in the north- ward and eastward components of wind velocity at Mauritius, from about 16 years' bihourly data. (&) Harmonic dial for the corresponding annual mean solar semidiurnal variations. Note the tenfold scale difference between the two diagrams. ent. The speed scale in Fig. 13a (lunar) is ten times more open than that for Fig. 136 (solar). The diagram Fig. 13a is, of course, not well determined. The corresponding semidiurnal paths of Mauritius air particles due to these oscillations are similar in form and orientation to the ellipses of Fig. 13, which will rep- resent these paths if all the time marks are advanced by three hours, and if the speed-scale is changed to a length-scale r/2Tr times as great, where T denotes the duration in seconds of the (solar or lunar) half day. This factor is 6876 for the solar diagram 136, and 7114 for the lunar diagram Fig. 13a. The distance scales are indicated on the left of each diagram. The extreme de- parture of any air particle from its mean position, at Mauritius, owing to these oscillations, is about 23 km for Ss and about 1 km for Li. The Lunar Tidal Rise and Fall of the Ionospheric Layers. It has long been inferred from the evidence of the geomagnetic variations that there are horizontal lunar tidal currents in the ionosphere, the ionized elec- trically conducting region of the high atmosphere, con- taining at least two distinct layers, the E-layer at about 100 km height, and the F-layer at about 250 km. The first direct determination of the lunar tidal rise and fall of the high atmosphere was made in 1939 by Appleton LUNAR. Fig. 13.—Diagrams based on Fig. 12, showing in plan the wind velocities at each lunar or solar hour (morning and afternoon) associated with the lunar and solar semidiurnal variations of wind at Mauritius. The velocity at each hour is repre
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